Apple Pencil 2

The second generation Apple Pencil is only compatible with iPad models that feature an inductive/magnetic charging dock that is explicitly designed for pairing/charging the second generation Pencil. 

The iPad10 does not have an inductive charging dock - principally as the front-facing camera has been relocated to the centre of the long-edge of the screen - and now occupies the internal cavity that might otherwise house the inductive charging dock components. As such, the iPad10 instead supports the first generation Apple Pencil that is paired and charged via the iPad’s USB-C port.

As for the special USB-C/Lightning Adapter, this adapter is included within the box of new first generation Pencils. If purchased directly from Apple, a new Pencil will include the adapter. Older stock, purchased from other retailers, may not include the Adapter.

For owners of existing first generation Pencils, or for purchasers of old-stock Pencils, the special adapter is available as an accessory:

• USB-C to Apple Pencil Adapter

https://store.apple.com/uk/xc/product/MQLU3ZM/A

It is what it is. Only apple knows for sure and they frown upon speculation. Chances are there’s some chip or communication protocol difference.